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MAGNESIUM BASE CASTING ALLOY Filed April 3, 1963 Magnesium m? ,4 v m9 21% ab .AVA a; 7% AVA AVAVAVA ay AVAVAVA AVAVAVAVAY $93M. YAVAVAVAVA AYAVAYAV VAAVAVA AVAYAV o v VA v VAYAVA 5" 11 I e Q vvvvv v vvv -4 a Colo/oer WI. fierce/7f co n oer g h INVENTORS. was-532$ nrronuzYs i United States Patent "ice 3,125,443 MAGNESIUM BASE CASTING ALLOY George S. Foerster, Midland, and Francis L. Burkett, Breckenridge, Mich, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed Apr. 3, 1963, Ser. No. 270,245 4 Claims. (Cl. 75-468) This invention relates to alloys of magnesium and particularly concerns a magnesium base alloy having particular utility as a casting alloy.

.Various magnesium base alloys, such as, for example, AZ63A, AZ92A and AZ91B (A.S.T.M. designation) have a reasonably good combination of mechanical properties such as strength with castability properties such as fluidity, ductility, resistance to cracking and surface appearance. None of these alloys, however, possess the castability necessary to, for example, cast articles having complex configurations. Illustrative of this is the fact that the alloy AZ91B tends to crack if cast into such shapes.

The primary object of the present invention, therefore, is to provide a magnesium base alloy having excellent castability and mechanical properties thus having special utility as a casting alloy.

The above and other objects and advantages have been found obtainable by alloying with magnesium both aluminum and copper within a particular range of proportions. Generally, it has been found that by alloying with magnesium aluminum in an amount of from about 1.0 to about 14.0 percent by weight and copper in an amount of from about 13 to about 30 percent by weight of the resulting alloy, a magnesium base alloy is obtained generally possessing excellent fluidity, ductility, and strength with respect to casting. The specific composition of the present alloy, however, is graphically illustrated in the accompanying drawing which shows a triangular coordinate graph in which percent aluminum, copper and magnesium in the alloy is plotted, the composition involved lying within areas which are further defined below.

The amounts of aluminum and copper, the balance by difference being magnesium, which have been found satisfactory in the alloy of the present invention are shown graphically in the single figure of the appended drawing, the polygon ABCD thereof, bounded by lines AB, BC, CD, and DA, referring to the broad composition range within which the desirable properties of the present alloy, as stated above, are obtained. The preferred range of amounts of aluminum and copper which may be employed in the alloy of the present invention is also shown in said drawing as the area EFGH bounded by lines EF, FG, GH and HE. Compositions represented by the area EFGH correspond in general to a range of aluminum in the alloy of from about 2 to about percent and a range of copper of from about 15 to about 26 percent, the balance of the alloy by diiference being magnesium.

It is generally known in the art that the fluidity and resistance to hot cracking of the binary magnesium base magnesium-aluminum alloy increases with increasing aluminum content. Such alloys, however, tend to be brittle. Similarly, the binary magnesium base copper alloys containing about 15 percent by weight, or more of copper, are also fluid, but also tend to be brittle. It is surprising, therefore, that when both copper and aluminum are alloyed together with the magnesium base metal to form the ternary magnesium base alloy as provided 3,125,443 Patented Mar. 17, 1964 2 under the present invention, a fluid, ductile and crack resistant alloy is thereby obtained, thus being highly suitable as a casting alloy for articles having intricate shapes.

Small amounts of other alloying constituents conventionally employed in magnesium base alloys may also be used in the present alloy, provided it does not significantly impair the improved castability of said alloy obtained under the present invention.

The term magnesium as used herein refers to the pure metal and alloys thereof having less than about 1.0 percent by weight of other constituents therein either as additions or as unavoidable impurities.

in preparing the alloy of the present invention, commercial grade magnesium is melted under a suitable halide flux cover, using conventional melting and alloying techniques as practiced in the magnesium art, and the copper and aluminum in the desired proportions as shown on the graph are added thereto as small ingots or chunks at a temperature sufiicient to dissolve said additions, as for example, a temperature of from 1250 to about 1350 F. The so-prepared melt is then cast into a heated mold having the desired cavity configuration as in die casting, the mold being heated to a temperature of from about 300 to about 700 F., or more, such that solidification during poring in the smaller and irregular channels of the die cavity will not occur prior to completion of pouring and subsequent withdrawal of the heat source from the mold. After the mold is filled the contents thereof is allowed to cool sufficiently to solidify. The solidified cast article is then removed from the mold. In addition, the article so cast may be subsequently solution heat treated and aged to enhance its strength.

The alloy of the present invention may be cast into sand or permanent molds, or employed in operations using a cold-mold die casting apparatus as commonly used in the die casting The following examples serve to further illustrate the present invention.

Several magnesium base alloys containing aluminum and copper were prepared, each having the composition as indicated'in Table I, some as alloys of the present invention and the others as blanks for comparison purposes, by melting commercial grade magnesium at a temperature of about 1300 F. under a halide flux cover and adding thereto small chunks of aluminum and copper in the amount required to produce the desired alloy composition. The halide flux used comprised about 34% KCl, about 31% MgCl about 12% CaF about 13% MgO', and about 10% BaCl A permanent mold having the cavity configuration of a 4 inch diameter test bar was heated to a temperature of about 540 'F. and the soprepared alloys cast therein. These bars were then tested for percent elongation (percent B) (using a 2 inch gauge section), tensile strength (TS), and tensile yield strength (TYS) (at a 0.2% offset) in the :as-cast condition, after solution heat treatment, and after solution heat treatment with subsequent aging, at the temperatures and times as indicated in Table I, which in addition sets forth the results of these tests.

It should be understood that other heat treatments and aging conditions than those indicated in Table I can be employed with respect to the alloy of the present invention in order to obtain, for example, greater age hardening and higher strength.

Table I After Solution Heat Treating After Solution Heat Composition As Cast for 16 hrs. Treating and Agin 24 Hrs. at 350 F.

Example 1,000 psi. 1,000 psi. 1,000 psi. Percent Percent Percent At'lemp, Percent Percent Al Cu E F. E E

TYS TS TYS TS TYS TS (Blank A) 15v 0 0 0 21 28 750 0 18 25 l 25 20 (Blank B) s- 0 l5. 0 0 22 22 870 0 0 l3 0 0 13 (Blank C) 3. 3 11.7 2 18 25 970 2 l2 2l 2 14 24 (l 4.4 15.6 1 24 31 970 5 14 32 5 16 31 (2)." 5. 5 19. 5 l 27 38 970 4 10 81 4 18 34 1 Balance, magnesium. In Table I above, Blanks A and B show that magnesium base alloys which contain high concentrations of either aluminum or copper possess no measurable degree of duetility, that is, the percent elongation shown for these 9 alloys is for practical purposes zero. Blank C, having a composition not within the range of the present invention, though ductile, does not have nearly the strength of the alloys of the present invention, illustrative of which are the alloys in Examples 1 and 2, nor the increased ductility of the said alloys in the examples in the heat treated condition. Examples 1 and 2 on the other hand illustrate the superior ductility and strength of the alloys of the present invention indicating its high desirability and utility as a casting alloy.

We claim:

1. A magnesium base alloy consisting essentially of aluminum and copper, the balance being magnesium, said alloy having a composition by weight within the composition range represented by the area ABCD, bounded by lines AB, BC, CD, and DA, of the graph in the appended drawing.

2. A magnesium base alloy consisting essentially of aluminum and copper, the balance being magnesium, said alloy having a composition by weight within the composition range represented by the area EFGH, bounded by lines EF, FG, GH, and HE, of the graph in the appended drawing.

3. A magnesium base alloy consisting essentially of about 4.4 weight percent aluminum, and about 15.6 weight percent copper, the balance being magnesium.

4. A magnesium base alloy consisting essentially of about 5.5 weight percent aluminum and about 19.5 weight percent copper, the balance being magnesium.

References Cited in the file of this patent UNITED STATES PATENTS 1,729,339 Gann Sept. 24, 1929 1,793,023 Schmidt Feb. 17, 1931 2,314,024 Topping Mar. 16, 1943 FOREIGN PATENTS 293,359 Great Britain Jan. 31, 1929 

1. A MAGNESIUM BASE ALLOY CONSISTING ESSENTIALLY OF ALUMINUM AND COPPER, THE BALANCE BEING MAGNESIUM, SAID ALLOY HAVING A COMPOSITION BY WEIGHT WITHIN THE COMPOSITION RANGE REPRESENTED BY THE AREA ABCD, BOUNDED BY LINES AB, BC, CD, AND DA, OF THE GRAPH IN THE APPENDED DRAWING. 